#include <stdio.h>
int main(){
	float x, y;
	scanf("%f", &x);
	if(x < 1){
		y = x;
	}else if(x >= 10){
		y = 3 * x - 11;
	}else{
		y = 2 * x - 1;
	}
	printf("%0.2f", y);
	
}